PIC32MX: Driving a Stepper Motor - Revision history

NickMarchuk at 20:21, 1 March 2010

2010-03-01T20:21:21Z

JarvisSchultz: /* Circuit */

2010-02-16T19:25:08Z

Circuit

JarvisSchultz: /* Code */

2010-02-16T18:53:27Z

Code

JarvisSchultz: /* Code */

2010-02-09T02:55:00Z

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JarvisSchultz: /* Code */

2010-02-09T02:45:09Z

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JarvisSchultz: /* Code */

2010-02-09T02:38:34Z

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JarvisSchultz: /* Code */

2010-02-09T02:27:35Z

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JarvisSchultz: /* Code */

2010-02-09T02:26:34Z

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JarvisSchultz: /* Circuit */

2010-02-09T02:15:33Z

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JarvisSchultz: /* Code */

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-== Original Assignment ==
-'''Do not erase this section!'''
-Your assignment is to create code that reads a voltage from a potentiometer and controls a stepper motor to rotate at a proportional speed.  The middle range of the analog input (i.e., 1.65 V) corresponds to zero speed, the minimum is maximum backward speed, and the maximum is maximum forward speed.  You will create an interrupt service routine that is called every 500 microseconds.  Each time through the routine, you will add 1 to a counter.  When that counter (time, in units of 500 microseconds) exceeds the inverse of the desired speed (time per step), you will change the digital outputs controlling the stepper motor to the next position, depending on the direction of motion, and set the counter back to zero.
-To do this, you must create a function that takes the analog input, turns it into a speed, then turns it into an inverse of speed that the ISR uses.  Clearly the shortest allowable inverse of speed is 1 unit (500 microseconds per step).  But can your motor really do this, or does it just vibrate if you try to rotate that fast?  Based on your experiments, you should find the maximum speed that the motor actually tracks and set that as a constant.  Then 3.3 V and 0 V map to this speed, in opposite directions.
-You will use a geared stepper motor that we provide.
 == Overview ==

@@ Line 26: / Line 26: @@
 [[Image:General_Bipolar_H-Bridge_Drive_Circuit.JPG|thumb|350px|General H-Bridge Bipolar Drive Circuit|right ]]
-A bipolar stepper motor has two separate phases.  The steps are created by changing the direction of the current flow through each of the phases in the correct sequence.  In this circuit, one-half of an h-bridge is connected to each of the four leads of the stepper motor.  These h-bridge transistors are used so that the 3.3V available from the PIC32 can be used as control logic alone, and the primary current for the motor can be sourced from somewhere else.  These also help to isolate the motor from the PIC32.  A general image of this h-bridge setup can be seen at right.
+A bipolar stepper motor has two separate phases.  The steps are created by changing the direction of the current flow through each of the phases in the correct sequence.  In this circuit, one-half of an h-bridge is connected to each of the four leads of the stepper motor.  These h-bridge transistors are used so that the 3.3V available from the PIC32 can be used as control logic (for switching current direction in the motor phases), and the primary current for the motor can be sourced from somewhere else.  These also help to isolate the motor from the PIC32.  A general image of this h-bridge setup can be seen at right (adapted from [http://www.nmbtc.com/motors/pm-step/engineering/selection_pm/drivecircuit.html NMB's Website]).
 <br clear=all>

@@ Line 167: / Line 167: @@
 		count++;
 		// Set the current byte of the RS232_In_Buffer to be equal to data:
-		// strncpy(&data,&RS232_In_Buffer[j%20],1);
 		data = RS232_In_Buffer[j%20];
 		// Increment our variable for indicating which variable in the buffer we are reading

@@ Line 39: / Line 39: @@
 == Code ==
-The entire pastable code for the PIC32 is in the text box below, and a link can be found here: [[Media:PIC32_Stepper_Motor_Driving_Code_JSJW.c]].  Compiling this code and loading it onto the PIC32 is the bare-minimum that is required for controlling the stepper motor.  If this is the case, motor control is handled through some serial communication terminal program (hyperterminal, [http://www.chiark.greenend.org.uk/~sgtatham/putty/| putty], or [http://realterm.sourceforge.net/| realterm]). Be sure to match the baudrate (115200), the stop bits (1), the parity bits (none), and the data flow (none).  In the main function of the program it is possible for the user to extract the correct format for the motor control data.  But, for simplicity, it is summarized here as well.  A total set of control data consists of 10, 8-bit (one byte) ascii characters.  The first character is either an 's', 'd', or 'p'.  An 's' implies that the user simply wants to set a motor speed to some value; a 'p' tells the PIC that the user wants to control speed and position of the motor i.e. step this fast for this many degrees; and a 'd' tells the motor to stop right where it is.  The second byte is either an ascii '1' or '0'.  This byte sets the motor direction.  The next three bytes set the motor speed in steps per second.  The first byte is the hundreds digit, then the tens digit, then the ones digit.  The last five bytes are the number of steps the user wants the motor to step before stopping; these are decoded in the same way except the most significant byte is the ten-thousands digit.  If the user sends an 's' as the first byte, the contents of the last 5 bytes will not affect the motor's behavior; if the user sends a 'd', only the first byte is important.  As an example, let's say the user wants to the motor to drive 1000 steps in the positive direction (the actual direction will depend on how the motor is wired up) at a speed of 300 steps/ second.  Then the user would send the string 'p130001000' to the PIC.
+The entire pastable code for the PIC32 is in the text box below, and a link can be found [[Media:PIC32_Stepper_Motor_Driving_Code_JSJW.c| here]].  Compiling this code and loading it onto the PIC32 is the bare-minimum that is required for controlling the stepper motor.  If this is the case, motor control is handled through some serial communication terminal program (hyperterminal, [http://www.chiark.greenend.org.uk/~sgtatham/putty/| putty], or [http://realterm.sourceforge.net/| realterm]). Be sure to match the baudrate (115200), the stop bits (1), the parity bits (none), and the data flow (none).  In the main function of the program it is possible for the user to extract the correct format for the motor control data.  But, for simplicity, it is summarized here as well.  A total set of control data consists of 10, 8-bit (one byte) ascii characters.  The first character is either an 's', 'd', or 'p'.  An 's' implies that the user simply wants to set a motor speed to some value; a 'p' tells the PIC that the user wants to control speed and position of the motor i.e. step this fast for this many degrees; and a 'd' tells the motor to stop right where it is.  The second byte is either an ascii '1' or '0'.  This byte sets the motor direction.  The next three bytes set the motor speed in steps per second.  The first byte is the hundreds digit, then the tens digit, then the ones digit.  The last five bytes are the number of steps the user wants the motor to step before stopping; these are decoded in the same way except the most significant byte is the ten-thousands digit.  If the user sends an 's' as the first byte, the contents of the last 5 bytes will not affect the motor's behavior; if the user sends a 'd', only the first byte is important.  As an example, let's say the user wants to the motor to drive 1000 steps in the positive direction (the actual direction will depend on how the motor is wired up) at a speed of 300 steps/ second.  Then the user would send the string 'p130001000' to the PIC.
 Note: There are limits to how fast the motor can spin.  If the user sets the speed too high, the motor will just vibrate.  Some motors list their maximum speeds on the data sheets.  If the desired motor does not have this listed, a little bit of experimentation should yield the maximum speed.
@@ Line 419: / Line 419: @@
-As mentioned at the top, this code was designed to work with processing.  A user interface has been programmed and can be found [[Stepper_Motor.zip| here]].
+As mentioned at the top, this code was designed to work with processing.  A user interface has been programmed and can be found [[Media:Stepper_Motor.zip| here]].  This zip file contains the main code (Stepper Motor/Stepper_Motor.pde).  This folder should be unzipped to the default processing applications folder (something like ...My Documents/Processing).  The other folder (controlP5) contains the necessary library to execute this code.  It should be unzipped to ...My Documents/Processing/libraries.  Information on this library can be found [http://www.sojamo.de/libraries/controlP5/| here].

← Older revision		Revision as of 02:38, 9 February 2010
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	Note: There are limits to how fast the motor can spin. If the user sets the speed too high, the motor will just vibrate. Some motors list their maximum speeds on the data sheets. If the desired motor does not have this listed, a little bit of experimentation should yield the maximum speed.		Note: There are limits to how fast the motor can spin. If the user sets the speed too high, the motor will just vibrate. Some motors list their maximum speeds on the data sheets. If the desired motor does not have this listed, a little bit of experimentation should yield the maximum speed.
			[[Media:Example.ogg]]

← Older revision		Revision as of 02:27, 9 February 2010
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	The entire pastable code for the PIC32 is in the text box below. Compiling this code and loading it onto the PIC32 is the bare-minimum that is required for controlling the stepper motor. If this is the case, motor control is handled through some serial communication terminal program (hyperterminal, [http://www.chiark.greenend.org.uk/~sgtatham/putty/\| putty], or [http://realterm.sourceforge.net/\| realterm]). Be sure to match the baudrate (115200), the stop bits (1), the parity bits (none), and the data flow (none). In the main function of the program it is possible for the user to extract the correct format for the motor control data. But, for simplicity, it is summarized here as well. A total set of control data consists of 10, 8-bit (one byte) ascii characters. The first character is either an 's', 'd', or 'p'. An 's' implies that the user simply wants to set a motor speed to some value; a 'p' tells the PIC that the user wants to control speed and position of the motor i.e. step this fast for this many degrees; and a 'd' tells the motor to stop right where it is. The second byte is either an ascii '1' or '0'. This byte sets the motor direction. The next three bytes set the motor speed in steps per second. The first byte is the hundreds digit, then the tens digit, then the ones digit. The last five bytes are the number of steps the user wants the motor to step before stopping; these are decoded in the same way except the most significant byte is the ten-thousands digit. If the user sends an 's' as the first byte, the contents of the last 5 bytes will not affect the motor's behavior; if the user sends a 'd', only the first byte is important. As an example, let's say the user wants to the motor to drive 1000 steps in the positive direction (the actual direction will depend on how the motor is wired up) at a speed of 300 steps/ second. Then the user would send the string 'p130001000' to the PIC.		The entire pastable code for the PIC32 is in the text box below. Compiling this code and loading it onto the PIC32 is the bare-minimum that is required for controlling the stepper motor. If this is the case, motor control is handled through some serial communication terminal program (hyperterminal, [http://www.chiark.greenend.org.uk/~sgtatham/putty/\| putty], or [http://realterm.sourceforge.net/\| realterm]). Be sure to match the baudrate (115200), the stop bits (1), the parity bits (none), and the data flow (none). In the main function of the program it is possible for the user to extract the correct format for the motor control data. But, for simplicity, it is summarized here as well. A total set of control data consists of 10, 8-bit (one byte) ascii characters. The first character is either an 's', 'd', or 'p'. An 's' implies that the user simply wants to set a motor speed to some value; a 'p' tells the PIC that the user wants to control speed and position of the motor i.e. step this fast for this many degrees; and a 'd' tells the motor to stop right where it is. The second byte is either an ascii '1' or '0'. This byte sets the motor direction. The next three bytes set the motor speed in steps per second. The first byte is the hundreds digit, then the tens digit, then the ones digit. The last five bytes are the number of steps the user wants the motor to step before stopping; these are decoded in the same way except the most significant byte is the ten-thousands digit. If the user sends an 's' as the first byte, the contents of the last 5 bytes will not affect the motor's behavior; if the user sends a 'd', only the first byte is important. As an example, let's say the user wants to the motor to drive 1000 steps in the positive direction (the actual direction will depend on how the motor is wired up) at a speed of 300 steps/ second. Then the user would send the string 'p130001000' to the PIC.

	Note: There are limits to how fast the motor can spin. If the user sets the speed too high, the motor will just vibrate. A little bit of experimentation		Note: There are limits to how fast the motor can spin. If the user sets the speed too high, the motor will just vibrate. Some motors list their maximum speeds on the data sheets. If the desired motor does not have this listed, a little bit of experimentation should yield the maximum speed.

@@ Line 39: / Line 39: @@
 == Code ==
-The entire pastable code for the PIC32 is in the text box below.  Compiling this code and loading it onto the PIC32 is the bare-minimum that is required for controlling the stepper motor.  If this is the case, motor control is handled through some serial communication terminal program (hyperterminal, [http://www.chiark.greenend.org.uk/~sgtatham/putty/| putty], or [http://realterm.sourceforge.net/| realterm]). Be sure to match the baudrate (115200), the stop bits (1), the parity bits (none), and the data flow (none).  In the main function of the program it is possible for the user to extract the correct format for the motor control data.  But, for simplicity, it is summarized here as well.  A total set of control data consists of 10, 8-bit (one byte) ascii characters.  The first character is either an 's', 'd', or 'p'.  An 's' implies that the user simply wants to set a motor speed to some value; a 'p' tells the PIC that the user wants to control speed and position of the motor i.e. step this fast for this many degrees; and a 'd' tells the motor to stop right where it is.  The second byte is either an ascii '1' or '0'.  This byte sets the motor direction.
+The entire pastable code for the PIC32 is in the text box below.  Compiling this code and loading it onto the PIC32 is the bare-minimum that is required for controlling the stepper motor.  If this is the case, motor control is handled through some serial communication terminal program (hyperterminal, [http://www.chiark.greenend.org.uk/~sgtatham/putty/| putty], or [http://realterm.sourceforge.net/| realterm]). Be sure to match the baudrate (115200), the stop bits (1), the parity bits (none), and the data flow (none).  In the main function of the program it is possible for the user to extract the correct format for the motor control data.  But, for simplicity, it is summarized here as well.  A total set of control data consists of 10, 8-bit (one byte) ascii characters.  The first character is either an 's', 'd', or 'p'.  An 's' implies that the user simply wants to set a motor speed to some value; a 'p' tells the PIC that the user wants to control speed and position of the motor i.e. step this fast for this many degrees; and a 'd' tells the motor to stop right where it is.  The second byte is either an ascii '1' or '0'.  This byte sets the motor direction.  The next three bytes set the motor speed in steps per second.  The first byte is the hundreds digit, then the tens digit, then the ones digit.  The last five bytes are the number of steps the user wants the motor to step before stopping; these are decoded in the same way except the most significant byte is the ten-thousands digit.  If the user sends an 's' as the first byte, the contents of the last 5 bytes will not affect the motor's behavior; if the user sends a 'd', only the first byte is important.  As an example, let's say the user wants to the motor to drive 1000 steps in the positive direction (the actual direction will depend on how the motor is wired up) at a speed of 300 steps/ second.  Then the user would send the string 'p130001000' to the PIC.
+Note: There are limits to how fast the motor can spin.  If the user sets the speed too high, the motor will just vibrate.  A little bit of experimentation

@@ Line 35: / Line 35: @@
 [[Image:Bipolar Stepper Motor Drive Circuit JSJW.JPG|1080px]]
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-In the above circuit, pins D0-D3 of the PIC32 are used to as inputs to the h-bridge chip.  The timers in the code switch these pins high and low to step the motor.  U2TX and U2RX are connected to an RS232 cable that is correctly grounded and connected to a PC.  This cable is used for sending signals to the motor and receiving current motor step counts from the PIC.  An interesting note is that this circuit and corresponding code will work for other four-lead bipolar stepper motors as well.  If using another motor, the motor supply voltage simply has to be adjusted to match this motor.  Be careful not to exceed the limits of the h-bridge chip!
+In the above circuit, pins D0-D3 of the PIC32 are used to as inputs to the h-bridge chip.  The timers in the code switch these pins high and low to step the motor.  The motor's output leads need to be correctly connected to the h-bridge outputs.  Some motor manufacturers specify which color wires correspond to which phase, but some do not.  If unsure which wire is which, use a multimeter, and test the resistance of each of the pairs of wires.  When one pair shows a resistance that is significant, you know that these two wires are internally connected.  This means that they will either need to be connected to outputs 1 and 2 or outputs 3 and 4 of the h-bridge.  U2TX and U2RX are connected to an RS232 cable that is correctly grounded and connected to a PC.  This cable is used for sending signals to the motor and receiving current motor step counts from the PIC.  An interesting note is that this circuit and corresponding code will work for other four-lead bipolar stepper motors as well.  If using another motor, the motor supply voltage simply has to be adjusted to match this motor.  Be careful not to exceed the limits of the h-bridge chip!
 == Code ==